Coolant-circulating adjustable grinding tool



A. J. HOLMAN COOLANT-CIRCULATING ADJUSTABLE GRINDING TOOL J Filed Nov.13, 1951 Jan. 10, 1956 4 Sheets-Sheet ,l

Jan. 10, 1956 A. Ll. HOLMAN COOLANT-CIRCULATING ADJUSTABLE GRINDING TOOLFiled Nov. 13, 1951 4 Sheets-Sheet 2 EML A. J. HOLMANCOOLANT-CIRCULATING ADJUSTABLE GRINDING TOOL Filed NOV. 13, 1951 Jan.10, 1956 4 Sheets-Sheet 3 Jan. 10, 1956 A 1- HOLMAN 2,729,926

COOLANT-CIRCULATING ADJUSTABLE GRINDING TOOL Filed NOV. 13, 1,951 4Sheets-Sheet 4 IIHHIHIIHHHH "IIHIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII United States Patenti() COOLANT-CIRCULATIN GADJUSTABLE GRINDING TOOL Arthur J. Holman, Brighton, N. Y.

Application November 13, 1951, Serial No. 255,914

9 Claims. (Cl. Slt-207) My invention relates to apparatus and methodsfor grinding curved surfaces on glass or other transparent materials andmore especially to precision generator grinding of lens blanks inmultiple by diamond milling over equatorial zones of a sphericalcarrier.` The present device is an improvement over the mechanismdescribed in copending patent application Serial No` 583,244, tiledMarch 17, 1945, which issued as Patent No. 2,510,113 on June 6, 1950,entitled Method and Machine for Grinding Lenses, of which I amcoinventor. The former apparatus does good grinding and serves well thepurpose for which it was designed, namely, continuous production offinish ground surfaces on lens blanks which are attached, one by one, tothe circular chuck holder before grinding and are removed therefrom, oneat a time, after grinding while the chuck holder is being rotatedcontinuously at suitable lens blank feeding rate. For polishing, theselens blanks must be remounted and, if they are polished singly, a verylarge number of spindles are required for volume production: if theground blanks are mounted in multiple on chucks, great skill andaccuracy are required to so mount them that the surface of each lensblank lies on a common spherical surface, otherwise there will be high,low and tipped surfaces and polishing time will be excessively long,particularly if the block is to be generator polished. If the block ispolished on an ordinary spindle polisher, polishing time is still longand rejections rise seriously with inaccurate mounting of ground blanks.

The principal object of the present invention is to provide an equipmentand a method of procedure to eliminate the necessity for remountingfinish ground lens blanks for polishing. When this is accomplishedsuccessfully, the line ground blanks can be polished very quickly andwith great accuracy in a suitable polishing machine employing thegenerating principle, a machine wherein the relative movements of thelens blanks and the polishing elements produce true curvature on thework and maintain correct curvature of the polishing elements. Thecomplete accomplishment of this principal object involves considerableinvention including an irnproved lens blank carrier, an improved diamondmilling generator adapted and arranged to handle the new lens blankcarrier and a new generator polishing machine which will polish quicklyall the tine ground lens blanks on the carriers as they come from thediamond milling generator. The present application covers the improveddiamond milling generator and the improved lens blank carrier, also `themethods by which they function. The new generator polishing machine isthe subject of my copending patent application Serial No. `739,011,tiled April 2, 1947, which issued as Patent No. 2,586,334 on February19, 1952.

A second object of this invention is to compensate, at periodicintervals, for wear on the grinding rings, thereby limiting the amountby which any batch of ground blanks may depart from the specifiedgrinding curve. It will be noted from examination of copending patentapplication, Serial No. 583,244 hereinbefore referred to, also mycopending patent application Serial No. 589,983, filed April 24, 1945,which issued as Patent No. 2,541,873 on February 13, 1951, for LensGrinding Tool and Method, that, as abrading material is Worn away, bycontinued grinding of lens blanks, the bore of the grinding rings willbecome enlarged. As a result, each successive lens blank is ground to avery slightly longer radius of curvature. With suitable diamond millingrings, it is expected that several hundred lens blanks can be ground foreach one thousandth inch of wear on the grinding rings, nevertheless,when each diamond milling generator grinds several thousand lens blanksa day, the total wear on the grinding rings in a months service willrepresent perhaps one sixteenth of a diopter difference in reti-actingpower of the curved surface of the lens. Improved mounting of thegrinding rings and a better ring structure permit adjustment of the boreof the grinding rings to limit, to any prescribed tolerance, thevariation in curvature of surface ground on lens blanks.

Another object of -this invention is to so form the grinding rings as toeliminate the necessity for spacer rings between the grinding ringsprogressively graded as lo grit size and cutting speed, therebysimplifying the structures, eliminating loose parts, improving thedistribution of coolant to the grinding areas, providing more effectivescavenging of ground materials and eliminating completely all shouldergrinding; i. e., grinding of lens blanks against the edge of a grindingring as distinguished from grinding of the blanks by the abradingmaterial covering the cylindrical bore of the grinding rings.Elimination of shoulder grinding is important for several reasons:shoulder grinding invariably deforms the grinding tool, splinters theblanks, makes scavenging of ground material more dflicult and decreasessubstantially the rate at which lens blanks may be fed to the grindingrings.

Another object of this invention relating to the generating of sphericalsurfaces, is to arrange the progressively graded grinding rings in suchmanner that lens blanks may be presented to the grinding rings from twodirections for combining rough and line grinding thereby permitting, (1)rotation of the carrier when fully loaded with lens blanks to be groundand, (2) complete grinding of all lens blanks on the carrier when thecarrier has been rotated through an angle of degrees.

A further object of this invention is to arrange the lens blanks on thesurface of the carrier in such manner that the carrier may be brought toits proper grinding posi-tion, within the grinding rings, withoutgrinding any lens blank down, at any point, to the depth of the ultimatelinsh ground surface. i

Further objects are to increase the rigidity of the structuressupporting the lens blank carrier so the carrier may be alwaysp-recisely positioned within the grinding rings and may be sosubstantially supported as to perm-it rapid feeding of lens blanks tothe grinding rings without causing chattering at the grinding surfaces;providing simple means for mounting the carrier in the supportingstructures, feeding the carrier into grinding position, rotating'thecarrier to feed lens blanks to the grinding rings, withdrawing thecarrier from grinding position and removing the carrier f-romitssupporting structures. q

Another object is to provide simple and effective means whereby ytoricsurfaces may be generated in multiple on a suitable lens blank carrierand may be polished subsequently in multiple.

Still another object of the invention is to provide simple means wherebythe carrier supporting and feeding structures may be easily and quicklyswung out of operating position to permit free access to the grindingrings for dressing, for adjustment to compensate for wear, or forreplacement.

The ultimate object of this invention is development of the method forrapid production of lens blanks finish ground in multiple to a commonspherical surface to speciiied curvature, said lens blanks beingsupported on a carrier suitable for insertion, subsequent to grinding,v

into a generator polishing machine wherein the fine ground sphericalsurface common to all lens blanks on the carrier may be polished quicklyand accurately without departure from true spherical form.

VThis diamond milling generator is fully enclosed so the coolant mostsatisfactory for rapid cutting may be used without messing up either theoperating personnel or the premises wherein the equipment is used.Coolant is fed to the grinding rings under pressure and is withdrawnfrom the generator, preferably, under partial vacuum to insure minimumleakage of coolant charged with ground material and maximum recovery ofdiamond grit loosened by grinding action. The machine is designed forlarge volume production and may be used for making precision optics butit will probably find its greatest use in the manufacture of ophthalmiclenses which are produced annualy by the millions in this country. Thedevice is not limited in design to any particular spherical or toriccurvature, as suitable structures rnay be built to generate anycurvature of lens surface from ten diopter to two diopter, or evenbeyond these limits, kand each particular size carrier will accommodatefrom l() to l5() percent more lens blanks than can be groundsuccessfully on cuhcks in conventional lens lapping machines or indiamond milling machines employing cup type wheels. Moreover, since thisdevice is a generating grinder, the yield of first quality product isbetter than 95 per cent whereas the current yield of first qualityproduct with lens lapping machines is'o'ften as low as 40 per cent andseldom exceeds 55 per cent in plants where inspection is critical and ahigh standard is maintained. Each lens made in this device is groundwith its optical center at the geometrical center of the blank, hencethere will be no discarding of lenses which will not center out inedging. Because of this fact, blanks should be edged to finish sizebefore being mounted on the lens blank carrier, thereby savingunnnecessary grinding and polish ing of lens surface which is eventuallyground away in the edging process. It is expected that this diamondmilling generator will effect a reduction of at least 50 per lcent incost of grinding ophthalmic lens blanks. Since the product of thisgenerator is finish ground lens blanks so supported in multiple on acarrier that their ground faces lie on a common spherical surface, thecarrier may be transferred to a generator polishing machine whereinpolishing of all blanks on the carrier may be effected, in oneoperation, quickly and without distortion. Thus, this method of grindingis effective, not only in reducing grinding costs, but also in reducingthe cost of subsequent polishing of the lenses. Y

Equatorial generator lt seems in order to point out the primarycharacteristic of this invention which distinguishes it from otherdiamond milling generators. During the recent war, many diamond millinggenerators were built which employed a cup type diamond milling tool. Inthese de vices, any cup tool will grind any and all curvatnres, withinreason, on lens blanks depending on the angle formed between the axis ofrotation of the tool and the axis of rotation of the lens blank in anyparticular set up of the generator. Essentially, these devices grindonly the polar cap of a sphere: this polar cap may consist of one singlelens blank or it mayinclude multiple lens blanks carried on a shell butin no event is it .possible vto grind successfully surfaces approachinga hernisphere in extent, i. e., surfaces comprising 180 degrees solidangle. In many respects, this polar cap grinding is similar to thegrinding done in ordinary lens lapping machines which operate today,basically, after the fashion used for centuries in grinding lenssurfaces. The distinguishing characteristic of Vmy new diamond millinggenerator is the fact that its grinds surfaces on a sphere adjacent tothe equator and does not grind at all on the polar caps because theseareas are utilized for me chanical support of the polar axis whereon thesphere is rotated. Specifically, then, my improved diamond millinggenerator is an equatorial grinder whereas all other diamond millinggenerators, as well as all lens lapping machimes, are polar capgrinders. Y

My device and the method of its operation may be best understood byreference to the drawings in which,

Fig. l is a plan View, at quarter scale, of the complete machine,

Fig. 2 is a front complete machine, k

Fig. 3 is an end elevation, at quarter scale, of the complete machine,

Fig. 4 is a partial vertical cross section, at half scale, in the planeof the axis of rotation of the tool.

Fig. 5 is an elevation, at half scale, of the lens blank carrier,

Fig. 6 is a plan View, at half scale, of part of the mechanism showingthe carrier supported in the lower half of its cradle with the upperhalf or" the cradle hinged back to carrier loading position,

Fig. 7 is a cross section, at full scale, through the grinding rings andthe adjacent portion of the tool supporting shell,

Fig. 8 is a cross section, at full scale, on line S-S of Fig. 7 showingcoolant circulation channels,

Fig. 9 is a cross section, at full scale, similar to Fig. 7 but showinga different arrangement of grinding rings,

Fig. l0 is a View, at full scale, of the portion of the abrading face ofa rough grinding ring showing shape of coolant circulation channels,

Fig. ll is a view, at half scale, of a fine grinding ring showing keystructure removable to permit periodic adjustment of the bore of thering,

Fig. l2 is a diagrammatic equatorial section, at full scale,illustrating positioning ol lens blanks on the spherical carrier,

Fig. 13 is a diagrammatic meridian section, at full scale, illustratingpositioning of lens blanks on the spherical carrier,

Fig. 14 is a diagrammaticA View, at half scale, of a special six curvelens blank carrier positioned within a five curve grinding ring forgenerating toric surface,

Fig. l5 is a sectional view, at half scale, on line IS-ii of Fig. 14showing positioning of axis of carrier with re* spect to grinding ringsfor generating toric surface.

Referring now more specifically to the drawings in which like referencenumerals indicate like parts, a base 1 (Figs. l, 2, 3 and 4) of heavycast metal is provided with two sets of integral machined bosses whereonare securely held and'accurately aligned bearing brackets 2 and 3 eachof'which houses a precision cylindrical roller bearing as indicated at 4(Fig. 4). A rotating tool unit, comprising hollow shaft 5 and toolsupporting shell 6 suitably press fitted or shrunk together as shownwithin bearing 4, is journaled in bearing brackets 2 and 3, and a pulley7 arranged for multiple V belt drive is suitably secured to shaft 5.Tool supporting shell 6 has an accurately machined cylindrical bore atits end of larger diameter wherein are snugly fitted, to prevent turningwithin the bore, multiple grinding rings comprising, from left to right(Figs. 4 and 7 j, rough grinding ring 3, fine grinding ring 9, and asecond rough grinding ring iti which is exactly like rough grinding ringS in composition and structure. A flanged retaining ring 11, secured tothe end of tool supporting shell 6 by suitable screws, serves to retainthe grinding rings in proper operating elevation, at quarter scale, Vofthe ariane position n the tool supporting shell. Grinding rings 8, 9 and10, collectively, comprise the diamond milling tool. The tool supportingshell is enclosed in a split housing, lower portion 12 (Figs. 2 and 4)being secured by suitable bolts to machined pads on base 1 and upperportion 13 being secured to lower portion 12 by suitable bolts, all asshown in Fig. 2. A flanged ring 14, containing an accurate bore centeredon the axis of rotation of tool supporting shell 6 and having an outerface square to said axis, is secured by suitable screws and a anged fitto upper and lower portions 13 and 12 of the split housing.

Coolant circulation Free circulation of coolant to the tool is suppliedin the following manner: A bore 15 (Fig. 4) which runs the length ofhollow shaft S, carries coolant, supplied from a suitable source througha connection (not shown) with the outboard end of shaft 5, to thecircular chamber 16 in the hub of tool supporting shell 6, circularchamber 16 being formed partly by the inner end of shaft 5, partly by aplug 17 closing the bore in the hub of tool supporting shell 6, andpartly by an annular recess turned in the hub of tool supporting shell6. From circular chamber 16, coolant flows through a plurality of holesdrilled in the body of tool supporting shell 6 all the way to the innerface of flanged retaining ring 11 which covers the ends of these drilledholes. In four axial positions under the grinding rings, saw cuts 18(Figs. 4, 7 and 8) are made in the tool seating bore of tool supportingshell 6 into each drilled hole to a depth of half the diameter of thedrilled hole. Rough grinding rings 8 and 10, composed of sinteredpowdered metal, are formed on their annular faces, as shown in Fig. 8,with curved recesses 19 extending each way from each drilled hole intool supporting shell 6, and with radial semicircular depressions 20(Fig. l) which connect curved recesses 19 with the abrading surfaces ofthe rough grinding rings. Thus, after the multiple grinding rings havebeen inserted in the tool supporting shell 6, there are many passagesfor circulation of coolant distributed uniformly across the face andaround the circumference of the abrading surface of the diamond millingtool. Coolant flowing to the right from the grinding tool (Fig. 4) willfind its way over tool retaining ring 11 into the tool housing; coolantflowing to the left will pass into the housing through holes throughtool supporting shell 6 as shown in the cross section at top of Fig. 4.All coolant will be withdrawn under partial vacuum from the tool housingthrough the opening in the bottom thereof.

Elimination of shoulder grinding In cases where an unusually largeamount of `glass is to be removed from the surface of lens blanks orwhere fused bifocal flint blanks are to be ground as showndiagrammatically in Fig. 12, it is preferable to arrange the grindingrings as shown in Fig. 9, wherein ne grindingring 9 has on either side arough grinding ring 21 provided on each annular face with coolantcirculation depressions as in Fig. 8, and each rough grinding ring 21is, in turn, flanked with a rough grinding ring 22 provided with abeveled edge which is `first to contact lens blanks as they are fed tothe grinding tool.` This arrangement of tool elements in the toolsupporting shell can accommodate a grinding cut to the depth indicatedas b (Fig. 9) without direct shoulder grinding whereas the toolarrangement shown in Fig. 7 can accommodate a grinding cut only to depthc before shoulder grinding begins. While on the subject of shouldergrinding, it is well to point out the advantages gained by moldingcoolant circulation channels in the rough grinding rings versusemploying spacer rings to providecoolant circulation channels. lt willbe evident from examination of Figs. 8 and l0 that rough grinding ringsare in contact withannular faces of the iine grinding ring at all areasaround the circumference of the tool, except at areas 6 oppositesemicircular depressions 20, hence there is no cylindrical zone on theface of the abrading tool where no grinding takes place. if spacer ringsare employed between the grinding rings, then there: will be anongrinding cylindrical zone at the tool surface opposite each spacerring and `this will mean shoulder grinding against the annular faces offine grinding ring 9. This condition would cause rapid wearing of thefine grinding ring, due to overloading, and would limit seriously therate at which lens blanks can be fed to the grinding tool.

Grinding ring wear From calculations based on data showing rate of wearof cup type diamond wheels, it is estimated conservatively that, in anequatorial diamond milling generator designed to generate six curvesurface (i. e., cylindrical bore of grinding tool is 1A', meter), whichis the machine illustrated in the drawings, about 600 lens blanks of 52mm. diameter will be ground for each one thousandth inch radial wear onthe grinding tool. Standard tolerance in ophthalmic lens productionseems to be 3556 diopter. Such tolerance on a six curve generator meansthat the bore of the grinding tool may increase, due to wear ingrinding,

by .0677 inch in diameter before it need be readjusted,

hence it is estimated that about 40,000 lens blanks may be ground beforenormal tool wear will exceed standard tolerances in lens surfacerefracting power. It is further estimated that the present equatorialgrinding generator will grind about 280 lens blanks per hour, hence thebore of the grinding tool will not require adjusting to cornpensate fornormal wear till the generator has operated 40,060/200 or approximately200 hours or 25 eight hour shifts which is about once each month if thegenerator is operated eight hours a day.

ln manufacturing diamond abrading wheels in which the sintered abradingmaterial is bonded to steel or other solid metal supporting structure,it has been found diflicult and uneconomical to make the diamondimpregnated layer much less than IAG inch in depth. In my improvedgrinding rings l propose to use sintered powdered metal throughout theentire ring, the diamond grit impregnation going to a depth of 1/s inchor less as shown by the broken line drawn across the grinding ringsections in Figs. 7 and 9, and by the circle drawn on the annular faceof ne grinding ring 9 shown in Fig. 1l.. I also propose to make thegrinding rings with a removable radial key section as shown in Fig. 8 at6i) and in Fig. ll at 61. When wear on the grinding rings approaches thelimit prescribed by tolerance in variation of lens surface curvature,the grinding rings are removed from the tooll supporting shell 6, theradial key section is removed from each grinding ring and is replaced bya narrower radial key section the width of which, circumferentially, isjust sufhcient to restore the grinding ring to its original bore whenthe ring is sprung so both its ends make contact with the new andnarrower radial key section. This operation will, of course, reduce theoutside diameter of the grinding ring and suitable shim rings will berequired around the grinding rings when they are reinserted in thecylindrical bore in tool supporting shell 6. A shim ring common to allgrinding rings in the tool may be used if it is suitably perforated topermit free flow of coolant through the tool. Combined shim rings andradial key section sets may be made up in advance and stocked for usewhen required. Sintered powdered metal grinding rings are easily moldedto provide coolant circulation channels as specified, the problem ofbonding the diamond grit impregnated sintered powdered metal on steel orother metallic supporting rings is eliminated, and sintered powderedmetal rings may be sprung easily in the manner hereinbefore describedand without damage to the diamond impregnated layer. Thus, my improvedgrinding ring structures are particularly advantageous for use in myequatorial diamond milling generator.

47 Spherical carrier Y A spherical lens blank carrier 23 (Figs. 4, 5 and6), with polar caps removed, is provided with a plurality of recesseswherein lens blanks lit with slight clearance, each recess having a ringseat 24 of somewhat smaller diameter than the recess whereon the lensblank rests g independently of its peripheral edge as shown in Fig. 13,

each ring seat being square to and centered on a radius of the sphericalsurface of the carrier and positioned at the same radial distance fromthe center thereof. lt is obviously advantageous to support molded lensblanks independently of their peripheral edges because, when lens blanksare so mounted, irregularities in molded peripheral edges cannot causetilting of lens blanks on their seats. Fig. shows the arrangement oflens blanks on the carrier as viewed in elevation. Fig. 6 shows thearrangement of lens blanks on the carrier as viewed in plan. Fig. 4shows the internal structure of the carrier which comprises a lowersection 25 and an upper section 26 between which sections is seatedequatorial ring gear 27, the latter' being prevented from rotating withrespect to sections 25 and 26 by dewel pin 28 which passes through gear27 and enters both sections of the carrier. A conical journal stud 29provided with an integral notched ring suitable to be engaged by asocket wrench, is seated on the bottom of a recess in upper section 26and lits snugly in an axial bore through upper section 26 and lowersection 25, the lower end of conical journal stud 29, of somewhatsmaller diameter, being threaded to fit accurately in the threaded boreof conical journal sleeve 30. The body of conical journal sleeve 3G isthe same diameter as conical journal stud 29 and fits snugly in theaxial bore through lower section 25 of the carrier; the head of conicaljournal sleeve 30 is the exact counterpart of the head of conicaljournal stud 29 and is seated on the bottom of a recess in the bottom oflower section V25. By using a pair of socket wrenches, conical journalsleeve 30 is screwed tightly on conical journal stud 29 thereby lockingall parts of lens blank carrier 23 together and also providing a pair ofaccurately aligned and corectly spaced axial conical journals. Conicaljournal stud 29 and conical journal sleeve 30 are, preferably, hardenedand ground all over. The body of lens blank carrier 23 may be made ofDow metal for lightness and strength and, in the larger sizes, thecarrier may be-made hollow.

lt will be observed from examination of Figs. 5 and 6, that the lensblanks are not equally spaced around the carrier 23, out at one greatpolar circle the spacing between lens blanks is greater than at anyother place on the surface of the carrier. Examination of diagrammaticFig. l2 shows the reason for this planned irregularity in spacing oflens blanks. In Fig. 12 the rectangle represents the outlines of thecross section of thc grinding tool with the line representing thegrinding surface extended bcyond each edge of the grinding tool. Theright half of Pig. l2 shows a lens blank edge at a distance d from agreat polar circle: the left halt` of Fig. l2 shows a lens blank edge ata distance e from the same great polar circle. The long arc tangent tothe grinding surface of the tool represents the curvature to be groundon the lens blanks, the other arc representing, in each case, thesurface of the unground blank. As the lens blank carrier is moved fromright to left, along the axis of rotation of the tool to the positionshown in Fig. l2, it is apparent that no part of the lens blank havingits edge at distance e from the great polar circle would ever contactthe grinding surface of the tool but the lens blank having its edge atVdistance d from the great polar circle has a portion of its surfacewhich projects above the line of the grinding surface of the tool, hencethat portion of the lens `blank would be ground o: as the carrier is fedalong the axis of rotation of the tool. lf the lens blank were mountedso that its edge was on the great polar circle, i. e., no spacingbetween lens blanks on the carrier, then that edge of the blank would begroundcompletely by the rough grinding-ring as the carrier is movedalong the axis of rotation of the grinding tool and subsequent feedingof lens blanks to the grinding tool by rotation of the carrier would noteiect any further grinding of this edge ofthe lens blank, even by thecentral tine grinding ring, thus a portion of the blank would not beline ground and hence this lens blank would have to be rejected. It isquite apparent, therefore, that it is advantageous to provide extra Widespace between lens blanks on the carrier at one great polar circle and,moreover, it is necessary to index the carrier to proper angularposition when it is inserted in the cradle as hereinafter noted.

Cradle for spherical carrier Lens blank carrier 23 is supported in aslidably mounted cradle (Figs. l, 2, 3, 4 and 6) in the followingmanner: Cradle 31, substantially spherical in forni, splits in twohalves at the equator, lowerl half 32 and upper half 33 being hingedtogether by hinge pin 34 which fits accurately in bores in two alignedbosses 35 carried at the ends of brackets integral with upper half 33,and also in bores in four aligned bosses 36 carried on a bracketintegral with lower half 32 of cradle 31. Also integral with lower half32 of cradle 31 is a pair of long parallel bosses 37, each containing anaccurate bore, the axis of which is parallel to that ofthe other boreand both axes lie in a plane parallel to the equatorial plane at whichcradle 3i is split. A pair of parallel guide rods 38 is a free butaccurate sliding lit in the bores in bosses 37 and serves to supportVslidably mounted cradle 31. While I have described cradle 31 assubstantially spherical in form, it Will be noted from Fig. 4 that lensblank carrier`23 is contained within cradle 31 and also that cradle 31must slide through the grinding tool to such position that the polaraxis of carrier 23 lies in the medial plane of the grinding tool.V Forthese reasons, lower half 32 andupper half 33 of the cradle are attenedinternally to provide suitable support for conical journal boxes 39 and40, respectively, wherein lens blank carrier 23 is journaled, also,lower half and upper half 33 of the cradle have an external contourwhich is cylindrical in form over those areas which must be so formed topermit the cradle to slide into operating position within the grindingrings. A cylindrical sufrace 41 and a flanged seat 42 are continuousover lower half 32 and upper half 33 of the cradle l and are,respectively, an accurate sliding iit in the bore and against the faceof flanged ring 14 attached to the casing enclosing the tool supportingshell, and serve to naled in a bore in lower half 32 of the cradle andcarries iixedly mounted on its other end Worm gear 45 (Fig. 4). A worm46, carried on shaft 47 meshes with worm gear 45. Through this geartrain, lens blank carrier 23 is rotated, by power supplied by a smalllmotor (not shown), to feed lens blanks to the grinding tool at optimumcutting rate.

A pair of brackets 48, integral with base 1 (Figs. l, 2 and 3), supportsat their ends bosses 49 which are bored to lit snugly on hinge pin 50. Atilting bracket 51 is bored to t snugly on hinge pin and carries a pairof bosses 52 containing parallel bores wherein parallel guide rods 38are a free sliding t. The other ends of parallel guide rods 38 'aresecured in bores in bosses 53 (Fig. l) which are integral with flangedring 14 mounted on the housing enclosing the tool supporting shell. Acontrol arm 54 is provided at one end with a boss bored to fit on hingepinV 34 and atV the other end with a boss bored to t on pin 55 by meansof which it is connected with lever arm 56 to which power is supplied bysuitable means (not shown) annesse" .9 Operation of equatorial generatorAlthough I have not shown mechanism for so doing, the operation of myequatorial diamond milling generator can easily, and should, be madeautomatic except for loading the lens blank carrier in its cradle beforegrinding and taking it out after the lens blanks are ground. Power issupplied through multiple V belts to pulley 7 to rotate the grindingtool at optimum cutting speed. For loading, cradle 31 is slid onparallel guide rods 38 all the way to the right (Figs. 1, 2 and 6) byoperation of lever arm 56 and upper half 33 of the cradle is swung opento the right as illustrated in Fig. 6. Lens blank carrier 23, fullyloaded with lens blanks to be ground as shown in Fig. 5, is then droppedcarefully into place in lower half 32 of the cradle and equatorial gear27 is meshed with pinion 43 in indexed position. Upper half 33 of thecradle is then swung back into closed position and a snap ring 62 orthreaded ring is placed over or screwed on the boss protruding from theleft side of the cradle (Figs. 4 and 6) thereby locking the two halvesof the cradle securely together and making the polar conical journals onthe carrier tit accurately in the polar conical journal boxes in thecradle. lt is to be noted here that conical type bearings will permithinged opening and closing of the cradle, also this type of bearing ismost satisfactory for aligningthe axis, centralizing the carrier in thecradle and accommodating thrust loads. By operation of lever arm 56,loaded cradle 31 is slid to the left on parallel guide rods 33,cylindrical surface 41 on cradle 31 enters the bore in iianged ring 14,circulation of coolant commences and those portions of all lens blankson the carrier which project beyond the cylindrical bore of the grindingtool will be ground away as the cradle continues travelling toward theleft and is iinally stopped when flanged seat 42 on the cra dle makescomplete contact with the outer face of flanged ring 14. The structuresare such that the medial plane through the grinding tool now passesthrough the polar axis of the spherical carrier, i. e., the grindingtool encircles the spherical carrier about a polar great circle. Thelens blank carrier is now in correct position for grinding the lensblanks carried thereon and power is applied to equatorial gear 27,through the means described, to rotate the carrier on its polar axisthereby feeding lens blanks to the grinding tool, the lens blanks on thecarrier at positions to the left of the medial plane through thegrinding tool will be fed to the grinding tool from one direction andthe lens blanks on the carrier at positions to the right of the medialplane through the grinding tool will be fed to the grinding tool fromthe opposite direction. Thus, the forces applied to the grinding tool inthe axial direction, by feeding of lens blanks to the tool, constitute acouple and are balanced. The forces applied to the carrier, throughrotative grinding by the tool, constitute a steady balanced torque,which tends only to rotate the cradle, not to displace it from itscentralized position. lt appears therefore, that, in this equatorialmethod of grinding, there are no unbalanced forces tending to set upvibration, hence lens blanks can be ground at maximum feeding rates andthe ground surfaces will be free from chatter markings.

l'f the apparatus has been accurately constructed and is maintained ingood condition, one half revolution (180 degrees) of the carriercompletes the rough and finish grinding of all lens blanks on thecarrier, circulation of coolant is then stopped, the cradle is returnedto its posi tion at the extreme right on guide rods 38, the snap ring orthreaded ring is removed from the projecting boss on the cradle, upperhalf 33 of the cradle is swung open and carrier 23 with its ground lensblanks is lifted out of the cradle and transferred to a cleansing bath,prior to being inserted in a cradle in a polishing generator. Thus, thegrinding cycle is completed.

Toric surfaces Interesting and thoroughly practical further applicationsof my improved equatorial diamond milling generators and methods may bemade in ophthalmic lens manufacturing plants for volume production oftoric surfaces. For instance, a special six curve lens blank carrier 57(Figs. 14 and 15) may be used in a five curve diamond milling generatorto rough and iine grind, successively and simultaneously, sixfive curvetoric surfaces in multiple. A six curve lens blank carrier cradleprovided with proper driving gear arrangement for rotating specialcarrier 57 would be required, also it would be necessary to have aproperly off set supporting and feeding structure for the cradle so thecarrier 57 would be brought into position with respect to tive curvegrinding rings as shown in Figs. 14 and 15. For this type of surfacegrinding, a rough grinding ring 58 provided with coolant cir culationchannels as in Figs. 8 and l0, would be required, also a line grindingring 59 which is one half the axial width of line grinding ring 9 (Fig.7) used for generating spherical surfaces It will be noted from Fig. l5,that the polar axis of special carrier 57 lies in the plane of the leftannular face of ine grinding ring 59 because it is the left edge of theabrading surface on the iine grinding ring which generates the finaltoric form on the surface of each lens blank as it passes thereunder.Subsequent polishing of the fine ground torio surfaces in multiple isdescribed in my copending patent application for polishing generatorspreviously referred to.

Adjusting grinding rings Whenever it becomes necessary to get at thegrinding rings, the screws (Figs. 3 and 4) retaining ilanged ring 14 inposition on the tool supporting shell housing are removed and flangedring 14 (Figs. l and 2) is pushed to the right as far as it will go, theguide rods 38 will slide through bores in bosses 52 until bosses 36 onthe cradle contact bosses 52 and then the entire cradle supportingstructure may be swung to upright position and out of the way as tiltingbracket 51 swings through 90 degrees on hinge pin 50. When work on thegrinding rings is completed, the cradle supporting structure is swungback into horizontal position, anged ring 14 is drawn all the way to theleft and reseated on the tool supporting shell housing, retaining screwsare inserted and screwed up tightly and the apparatus is again ready forgrinding operations.

Lens blanks edged to nnl size ln ophthalmic lens manufacturing plants ithas become standard practice to use lens blanks molded to 52 mm.diameter although first `quality lenses are seldom, if ever, required tocenter out to more than 44 mm. diameter. However, even with this widelatitude of 4 mm. on a side, many finished lenses now fail to meet firstquality requirements because they will not center out to 44 mm.diameter: this because blanks are tipped when mounted for second sidegrinding or because of excessive prismatic grinding of blanks mountedaround the periphery of large grinding shells. It is of interest to notehow much needless surfacing of glass can be eliminated when lenssurfaces are generated on blanks in such manner that the geometricalcenter of the lens is also its optical center. Since the area of acircle is proportional to the square of its diameter, the ratio of areasof 44 mm. and 52 mm. diameter blanks is equal to (44/52)2 or .717; sogenerator ground and polished lenses, if edged to finished diameterbefore surfacing, would save about 28 per cent of surface grinding andpolishing. Moreover, lens blanks stuck together' in sticks can be edgedat much less cost than can finished lenses which must be edged singly.The use of edged blanks in my improved. equatorial generator willrepresent further saving in cost of grinding rings and further reductionin grinding and subsequent polishing costs because an average of 25 percent more lens blanks can be accommodated on a carrier. For example, ona six curve carrier, as shown in the drawings,

' 1l sixteen 52 mm. diameter blanks are accommodated whereas twenty 44mm. diameter blanks can be equally well fitted on a six curve carrier.This would represent per Vcent more salable product from each generator.Edged blanks would permit further economies in operation: edged blanksseat better in carrier recesses and with less clearance, thus furthereliminating factors tending to produce inferior product.

In applying my improved equatorial diamond milling generator to lensmanufacture, it is not necessary to have a special size machine for eachcurvature to be generated. For example, in making ophthalmic lenses fromfour curve to ten curve, not more than six different machine sizes aredesirable, intermediate lens curves being ground by using grinding ringsof suitable bore in the next larger machine. For each desired curve tobe generated, carriers are equipped to accommodate that curve but itwill not be necessary to have a cradle size for each carrier size: insome sizes, a cradle may accommodate carriers varying in diameter up toa half curve. As has been stated hereinbefore, toric surfaces of variouscylindrical powers may be generated on any spherical curve generator bysubstituting suitable grinding rings and providing the machine with theproper carrier, cradle and off set support for the cradle. These specialitems of equipment represent but a small extra cost.

Prime advantages of equatorial generating method Engineers skilled inthe art of lens making will readily understand the principal advantagesmy improved equatorial diamond milling generator offers, most of whichhave been stated as objects of this invention. It is to be pointed out,however, that the greatest possible precision in lens grinding is to behad from this machine and for the very simple. reason that there cannotpossibly be any rolling off at the edges of the ground surface: thisbecause the grinding is done all around the blanks mounted on thespherical carrier and by grinding rings of precision form which do notand cannot become deformed through service. Since there are ground lensblanks located at both ends of many diameters of the sphericalcarrier,it is a simple matter to measure curve diameter by micrometer and knowprecisely, to a thousandth of an inch or closer if desirable, just whatcurvature has been generated on the lens blanks on each and everycarrier. These are prime advantages of the equatorial generating methodand render it most valuable in the production of matched lenses such asare required on the revolving lens wheel in my Optical Rectifier asdescribed in Letters Patent of the United States No. 1,957,457, datedMay 8, 1934. Y

In the manufacture of the highest grade optical surfaces forphotographie lenses and the like, it may be advantageous to rough grindthe blanks in one equatorial generator and fine grind them in another:it might even be worth while to intermediate grind in a second generatorbefore finish grinding in a third machine. Should this practice befollowed in precision optics manufacture, it is obvious that only onegrain size of diamond grit will bc used in each grinding generator. butmultiple grinding rings will still be required and the functioning ofthe generator will ce substantially the same as hereinbeforc described.In lother words, the equatorial generator will function equally well forany one particular fineness of grinding if the multiple grinding ringsshown in-Figs. 7 and 9 all contain the same diamond grain size.

The structures I have illustrated and described represent, for thepresent, the preferred forms of my device. lt is Vto be understood,however, that other mechanisms might be designed and constructed bythose skilled in the art, for` performing the essential functions of thepresent structures, namely equatorial grinding of multiple lens blanksmounted on a spherical carrier. The attached claims are drawnsufficiently broad to cover any and all devices of this character, alsothe methods of their use,

and it is the intention that the claims be so interpreted.

Having thus fully described my improved equatorial diamond millinggenerator, also my multiple lens blank carrier and methods of operationto produce curved surfaces on multiple lens blanks mounted on a carrier,what I claim is:

l. In an equatorial generator, a rotating tool unit comprising a hollowshaft and a tool supporting shell securely attached thereto, acylindrical bore in the end of said tool supporting shell, multiplecoolant circulating channels through said tool supporting shellconnecting withV the coolant channel through said hollow shaft, multiplesaw cuts in said cylindrical bore cut partly through said multiplecoolant circulating channels, a plurality of grinding, rings removablysupported in said cylindrical bore and provided with coolant circulationchannels connecting said multiple saw cuts with the abrading surfaces ofsaid plurality of grinding rings, and a tiange secured to the end ofsaid tool supporting shell to retain said grinding rings in operatingposition and to cover ends of said multiple coolant circulating channelsin said tool supporting shell.

2. in an equatorial generator, a rotating tool unit having a cylindricalbore fitted with a plurality of grinding rings of differing grit grainsize, said grinding rings being arranged in such order that thecentrally mounted grinding ring has the finest grit grain size, the twogrinding rings flanking said central grinding ring are next coarser ingrit grain size and the outer grinding rings are coarsest in grit grainsize, said outer grinding rings having beveled edges to provide forextra deep cuts without shoulder grinding.

3. In an equatorial generator, a rotating tool unit having a cylindricalbore fitted with a plurality of grinding rings of differing grit grainsize, said grinding rings being mounted in such order that grit grainsize increases progressively in both directions from the middle alongthe axis of rotation of said rotating tool unit.

4. In a rotating tool unit adapted and arranged for coolant circulation,diamond grit impregnated sintered powdered metal grinding rings havinginternal cylindrical abrading surfaces and concentric externalcylindrical seats and being mounted in multiple in a cylindrical recessin said rotating tool unit, alternate grinding rings being formed'withradial and connecting transverse channels in their annular surfaces,through which channels coolant may flow to said cylindrical abradingsurfaces when said grinding rings are mounted in said rotating toolunit.

5. In a rotating tool unit, an adjustable grinding ring comprising adiamond grit impregnated sintered powdered metal grinding ring'having aninternal abrading surface and a concentric Vexternal cylindrical seatsuitable for mounting in a cylindrical recess in said rotating tool unitand being formed with a radial key opening wherein-progressively thinnerradial key' sections may be substituted as required to compensate forincreased diameter of bore, due to wear, a diamond grit impregnateedradial key section, and a shim ring of such thickness that the radialends of said grinding ring press firmly against the sides of said radialkey section when said adjustable grinding ring is inserted in thecylindrical recess in said rotating tool unit.

6. In a rotating tool unit arranged for coolant circulation, a grindingring adjustable to compensate for wear, comprising a diamond gritimpregnated grinding ring having an internal abrading surface and aconcentric external cylindrical seat suitable for mounting in multiplein a cylindrical recess in said rotating tool unitpand being formed witha radial key opening wherein progressively thinner radial key sectionsmay be substituted as needed to compensate for wear, said grinding ringbeing formed also with connecting radial and transverse channels in itsannular faces through which coolant may flow to the abrading surfaceswhen grinding rings are mounted in multiple in said rotating tool unit,and a radial key section.

7 .t A coolant-circulating grinding tool for combined rough and tinegrinding, comprising a ne grinding ring and a rough grinding ring, eachprovided with cylindrical abrading surfaces mounted on a common axiswith an annular face of said ne grinding ring in contact with an annularface of said rough grinding ring, the contacting face of said roughgrinding ring being formed with connecting lateral and radial channelstherein through which coolant may fiow to the abrading surfaces of saidgrinding rings.

8. A coolantcirculating grinding tool for combined rough and finegrinding, comprising a fine grinding ring and a pair of rough grindingrings, each provided with cylindrical abrading surfaces, mounted on acommon axis in such manner that an annular face of each rough grindingring is in contact with an annular face of said ne grinding ring, thecontacting annular face of each rough grinding ring being formed withboth lateral and radial channels therein through which coolant may ow toush ground material etc. from the abrading surfaces of said grindingrings.

9. A coolant circulating grinding tool for combined rough and finegrinding, comprising multiple grinding rings of diiering grit grain sizemounted on a common axis with their annular faces in contact, theannular face of each coarser grinding ring which is in contact with anannular face of a finer grinding ring being provided with both lateraland radial channels through which coolant may ow to scavenge groundmaterial and loosened grit from the abrading surfaces of said grindingrings.

References Cited in the file of this patent UNITED STATES PATENTS150,799 Sutton et a1. May 12, 1874 553,225 Barnes Jan. 21, 1896 704,428Allen July 8, 1902 1,306,533 Friel June 10, 1919 2,105,896 Stubbs Jan.18, 1938 2,173,555 Hippie Sept. 19, 1939 2,270,209 Van der Pyl Jan. 13,1942 2,510,113 Holman et al. June 6, 1950 FOREIGN PATENTS 544,374Germany Feb. 17, 1932

